The present invention relates to the field of communications systems, and more particularly to navigation and tracking systems that provide real-time location and relative position information of all vehicles engaged in a given activity.
Presently, there are few electronic navigation systems that provide such real-time location and position information on a global basis. These systems invariably utilize satellites as signal sources, signal relays and position references. Such satellite systems fall into one of two types; active location systems and passive location systems. An active location system is one in which the equipment aboard the user craft (local user) transmits a signal back to the satellite in response to the interrogation from the satellite to determine its position information. On the other hand, a passive system is one in which the local receiver determines its position from receiving satellite signals alone. There is no need for a receiver in a passive system to send signals back to the satellites. This allows a passive system to simultaneously service a multitude of users without the need for a high transmission capacity. Consequently, the technology has settled on passive systems for general use.
One such passive navigation system is the Global Positioning System (GPS). The GPS plans to position a total of 18-24 satellites in orbit to provide navigation information anywhere on earth. When fully implemented, this system will be a universal positioning and navigation system that can provide three dimensional position accuracies to 10 meters, velocity to an accuracy of 0.03 m/s, and time to an atomic clock accuracy. Even though it is not yet fully deployed, the GPS system is already in wide use.
The basis for the GPS's accuracy in providing position information is having a receiver that can precisely measure the transit time of signals radiated from a plurality of GPS orbiting satellites. Depending on the position information required, a GPS receiver must utilize a certain number of satellites. To determine three-dimensional position information, the receiver must utilize signals from four different satellites. But, only three satellite signals are required to obtain two-dimensional position information (i.e. latitude and longitude).
Presently, GPS receiver units are installed in a variety of devices such as airplanes, ships, ground vehicles, and hand-held portable navigation sets. These receivers calculate the position coordinates of that unit's location and display its position as an alphanumeric digital readout of latitude/longitude or Universal Transverse Mercator (UTM) coordinates. None of these prior art implementations, however, provide a graphical display of the local unit's position and the relative location of other units in proximity to the local unit from the viewpoint of that local unit.
Consequently, those skilled in the art have recognized the need for a device that can provide a relatively real-time graphical display, from the local unit's viewpoint, of the position of remote units in proximity to that local unit. Such a display is particularly advantageous in that it does not warrant the complexity, size, and cost of color computer displays that require map information to show the position of remote devices with respect to each other from the satellite's viewpoint (as opposed to the local unit's viewpoint).
This technology is valuable for both tactical military and commercial applications such as tracking trucking fleets, police or medical emergency vehicles, airplanes taxiing on runways, or military armored vehicle maneuvering in a battlefield situation (which would help prevent fratricide).